Polarographic micro-electrodes are currently the only clinically applicable method to obtain pO2 directly, but they have some limitations and disadvantages when used in follow-up studies. On the other hand, EPR oximetry is suitable to monitor pO2. In methodological aspect, however, the agreement of pO2 values using both methods are important to use EPR oximetry. The pO2 measurements using EPR and electrode methods produced comparable results in the brain, muscle and tumor. EPR and electrode give similar pO2 values under anesthesiafrom the same area of measurements. The reasonably positive results are encoun tered to use EPR oximetry and give the choice of measurements of pO2 and it will expand research methodology and field, and give us the developments of understanding to the roles of pO2 in tissue.